One objective of the proposed projects is to study the effects of noise on the inner ear epithelia. Changes in the magnitude and pattern of hearing loss and cochlear damage will be determined in experimental animals as the parameters of exposure (frequency, intensity and duration) are systematically changes. Attempts will be made to elucidate the mechanisms of noise damage. Normal ears will be exposed to conditions with known mechanisms of action (e.g. changes in ionic environment) and the cellular alterations found in these ears compared to those in noise-exposed specimens. Also various electron microscopic tracers will be perfused through the different cochlear scalae in an attempt to determine whether or nor permeability of the cochlear duct changes after a damaging noise exposure. Another objective is to define the anatomical correlates of ischemia and other forms of hypoxia and recovery therefrom in the inner ear structures. The morphological changes which signify irreversible damage after repeated episodes of complete or partial anoxia will be identified. Using food-reward operant-conditioning techniques, pre- and post-exposure pure-tone audiograms will be determined for the noise-exposed animals and some of those in the perfusion experiments. Histological evaluation of the specimens will include detailed study of the plastic-embedded flat preparations by phase contrast microscopy so that counts of damaged or missing sensory cells can be made and percentages calculated. Selected areas of pathological interest will then be sectioned for light or electron microscopic study.